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Blog

Filtering by Tag: Galaxy formation

"The impact of feedback and the hot halo on the rates of gas accretion on to galaxies" - Correa et al. (2018)

Alan Duffy

My former student, and now high flying postdoctoral researcher at Leiden University, Dr Camila Correa answered one of the basic questions in galaxy formation in this paper - how does gas get to the galaxy from the larger Universe? The simple answer is, it depends. Essentially the bigger you are the more gas you can pull in, until you get to something the size of our Milky Way, when the `accretion'  rate of material infalling then flattens out. This picture is complicated as the hot gas halo surrounding a galaxy is responsible for preventing new material from infalling as it shocks against the hot halo. The amount of the hot halo depends on the type of energetic events within a galaxy, be it exploding stars (supernovae) or accreting black holes (AGN). A beautiful bit of work that will inform theorists and observers for years to come!

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"Dark-ages reionization and galaxy formation simulation XIV: Gas accretion, cooling and star formation in dwarf galaxies at high redshift" - Qin et al. (2018)

Alan Duffy

One of the challenges in exploring the early universe is that it is so far from us, as we peer billions of light years away to see it as it was all those billion of years ago. That means small faint objects, like dwarf galaxies, that we suspect do the main job of reionising the universe are nearly impossible to measure. It's therefore a challenge to constrain the DRAGONS universe; one way is to wait until little things build into bigger things that you then can see and test those. The other is to constrain the Semi-Analytic Models against the hydro simulations of Smaug. In this astounding exhaustive and thorough review of the two techniques my student Yuxiang Qin explores the connections and learns what to modify in one to mimic the other. Just being on top of one of these techniques would considered impressive in a PhD, to do both is truly exceptional. 

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"The formation of hot gaseous haloes around galaxies" - Correa et al. (2018)

Alan Duffy

My old student Camila Correa continues to revolutionise the basic fundamentals and assumed wisdom of galaxy formation. In particular she thoroughly explored the simple idea that infalling gas will shock against the other gas floating around the galaxy. In this paper, Camila used the EAGLE simulation series to explore the way in which exploding stars (supernovae) or feeding blackholes (AGN) impact that development of the hot halo. Essentially the supernovae ejects gas from the galaxy into nearby space, presenting a bigger target to infalling material, and hence makes the hot halo easier to form. The blackholes on the other are more energetic and eject material from the halo entirely, making it harder to form the hot halo in the first place. Overall, Camila showed that there was a critical halo mass above which the hot halo will form, around a half the size of the Milky Way at the present day.

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"Dark-ages reionization and galaxy formation simulation XI: Clustering and halo masses of high redshift galaxies" = Park et al. (2017)

Alan Duffy

Where do galaxies form? how big can they be? Do galaxies 'prefer' to lie closer to one another or further apart? And how does all of this change across Cosmic Time? These are just some of the questions Jaehong Park asked within the DRAGONS team in this paper. To explore how galaxies grow near one another, known as clustering, and how they grow within the larger dark matter halos, aka bias, Jaehong analysed countless thousands of simulated galaxies. Compared against one another, at different outputs from the simulated universe of DRAGONS, the overall distributions were robustly analysed with statistical tools that then permitted comparison with images from Hubble. The work is a staggering scale and one I'm sure Jaehong will be proud of for many years to come.

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